256 Prof. M'Intosh's Notes from the 



been intruding, and is easily recognized by the nnroerous 

 nuclei. The halves of the lip-organ in the lower chamber 

 are becoming continuous and, fusing, form a dense cylinder 

 with only a chink in the centre, the nuclei of the cells being 

 situated near the external border. The alimentary canal in 

 the upper region occupies more than half the area within the 

 body-wall. At this level the hypoderm is thickest laterally 

 and has increased ventrally with the downward progress of 

 the nerve-cords, the lip-organ is now solid in section and 

 smaller, whilst the canal above has increased in size, and 

 a central chamber of different cellular structure makes its 

 appearance, whilst by-and-by only muscular fibres occupy 

 the place of the lip-organ inferiorly, and a coelomic space 

 occurs at each side. The nerve-cords touch and soon fuse. 



The alimentary canal now takes a median position in 

 the body-cavity, with a dorsal and a ventral mesentery, 

 and it occupies a large space. The thinning of the dorsal 

 longitudinal muscles in the mid-lateral region indicates a 

 differentiation, whilst a considerable mass over the ventral 

 nerve-cord and a thinner layer on each side represent, the 

 longitudinal ventral muscles. The mucous glands now 

 appear toward the lower region of the ccelom, and they 

 seem to have the same structure (PI. Xll. fig. 28) as in 

 Owenia, and to open by similar wide ducts. The dorsal 

 and ventral blood-vessels in the respective mesenteries are 

 large. The hypoderm at this level is thick all round, espe- 

 cially veutially, where the nerve-cords are in juxtaposition, 

 and the dorsal and ventral longitudinal muscles are thicker 

 and better differentiated (PI. XII. fig. 29). The alimentary 

 canal next presents various wrinkles ; and a pale band passes 

 from each side of the nerve-cords (which are proportionally 

 large) outside the basement-layer, as if extension were 

 indicated. The alimentary canal is thrown into deep folds, 

 as if a stomachal or gizzard-like part existed in the lateral 

 regions, whilst the dorsal and ventral arches have the 

 ordinary raucous structure; then considerable vertical con- 

 striction occurs, the dorsal and ventral arches disappear, 

 and a vascular sinus is established laterally. Thereafter the 

 gut is pointed above and is split into two lobes ventrally, 

 with muscular bundles in the gap. The latter (gap) by-and-by 

 disappears, the canal enlarges, the lumen is much filled up 

 with the denize coating of cells, and the vascular sinus around 

 it is continuous in the sections (PL X. fig. SO). Externally 

 at this level the hypoderm is massive ventrally, thins off 

 laterally, and again becomes thin dorsally. The longitudinal 

 muscular coat is thinner, and fibres radiate from a little 



